1. Field of the Invention
The present invention relates to an apparatus intended to use superconductivity and suitable for use as electric power, transportation, mechanical power, high energy and electronic machines.
2. Description of the Related Art
Practical applications are known of machines and other apparatus relying on superconductivity, and each housing a superconductor of the metallic type selected from NbTi, NbZr, Nb.sub.3 Sn, V.sub.3 Ga, Nb.sub.3 (GeAl), Nb, Pb, Pb - Bi and the like and cooled by liquid helium (which will be hereinafter referred to as L - He). Such applications include, for example, energy and signal transmission lines such as power and communication coaxial cables; rotary machines such as the motor and generator; magnet-using machines such as the transformer, SMES (Superconducting Magnetic Energy Storage), accelerator, electromagnetic propulsion train and ship and magnetic separator; magnetic shields; electronic circuits; elements and sensors which can be cited as concrete examples of the superconductivity-using apparatuses or machines.
Each of these superconductivity-using apparatuses or machines often uses a single superconductor. There has also been developed the high-bred magnet wherein two kinds of superconductors which are NbTi and Nb.sub.3 Sn or NbTi and V.sub.3 Ga are used as a part of the small-sized magnet and the superconductor of Nb.sub.3 Sn or V.sub.3 Ga, higher in critical magnetic field, is located on the side of high magnetic field.
The superconductivity-using apparatuses or machines can use a large amount of high density current and they can also be operated under the condition that their electric resistance value is zero or under permanent current mode. It can be therefore expected that they are made smaller in size and save energy to a greater extent. There has also been developed the superconductor of the ceramic type which can be used under the cooling condition of relatively high temperature realized by liquid nitrogen (which will be hereinafter referred to as L - N) or the like cheaper than L - He.
However, the conventional superconductivity-using apparatuses or machines had the following drawbacks.
1) Extremely low temperature realized by L - He is essential. This makes the apparatuses or machines complicated in structure and it is therefore difficult to make them small in size. Further, they are expensive and have a limitation in their use.
It is therefore desired that an apparatus, smaller in size, having a higher ability and new other functions is realized. If the superconductivity-using apparatuses or machines can be made smaller in size, their heat flowing area will become smaller. This enables their refrigerating capacity to be reduced to a greater PG,4 extent.
2) As compared with the metal superconductor, the ceramic superconductor is 1/10-1/100 or still lower than these values in the carrier density of superconducting current. Therefore, its grain boundary barrier is larger and its coherent length is shorter. This makes it impossible for the ceramic superconductor to obtain a current density high enough to be used for industrial machines. Particularly because of its thermal fluctuation and flux creep caused under high temperature, it cannot create a stable superconducting condition.